Ok, the auto-import feature has been a personal favourite, which I had to defend and support in the tracker for quite a while, so please allow a little rambling.
Please implement it nicely in the first release - chances are you won't get back to it in the next release and people won't ever use it much (as I think happened with column selection mode).
Auto-import gets in the way, imports wrong class: IDEABKL-2331
Auto-import inserts wrong import statements: IDEABKL-2448
Auto-import could decide on correct imports automatically, but doesn't: IDEABKL-2236
And a couple of others.
The most important thing in my opinion is to never import wrong classes and to refrain from wanting to import a class while I am still typing on its name - only trigger auto-import when the word is completed (i.e. after caret is no longer adjacent to the word).
If this is implemented, I think auto-import should be ON by default. It will make for a very pleasant surprise when a newcomer evaluates Idea (else she will probably only find it after having already bought Idea and using it for quite a while).